U.S. patent application number 10/435063 was filed with the patent office on 2003-11-13 for optical switch.
Invention is credited to Kato, Yoshichika.
Application Number | 20030210853 10/435063 |
Document ID | / |
Family ID | 29244230 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030210853 |
Kind Code |
A1 |
Kato, Yoshichika |
November 13, 2003 |
Optical switch
Abstract
There is provided an optical switch configured such that the
electrode-to-electrode distance can be easily set to a desired
distance and a plurality of protrusions or an electrode pattern for
preventing the sticking from occurring can easily be formed on the
surface of a fixed electrode substrate on which a fixed electrode
is formed. There is prepared an upper substrate comprising an
insulation layer, a thick single crystal silicon layer formed on
the top surface of the insulation layer, and a thin single crystal
silicon layer formed on the bottom surface of the insulation layer.
A movable plate-like electrode and a plurality of flexible
beam-like members for supporting the movable plate-like electrode
to be displaced vertically are formed in the thin single crystal
silicon layer. By applying an etching to the thick single crystal
silicon layer, a plurality of the optical fiber securing grooves
are formed as well as a plurality of micro-mirrors erecting from
the movable plate-like electrode are formed on the thick single
crystal silicon layer. The upper substrate is mounted on a lower
substrate comprising a fixed electrode substrate and a fixed
electrode formed on the top surface thereof, through a spacer
interposed therebetween, thereby to juxtapose the fixed electrode
and the thin single crystal silicon layer substantially in parallel
with each other and in opposed manner with a predetermined gap
therebetween.
Inventors: |
Kato, Yoshichika; (Tokyo,
JP) |
Correspondence
Address: |
GALLAGHER & LATHROP, A PROFESSIONAL CORPORATION
601 CALIFORNIA ST
SUITE 1111
SAN FRANCISCO
CA
94108
US
|
Family ID: |
29244230 |
Appl. No.: |
10/435063 |
Filed: |
May 9, 2003 |
Current U.S.
Class: |
385/18 ;
385/17 |
Current CPC
Class: |
G02B 6/3692 20130101;
G02B 6/357 20130101; G02B 6/3546 20130101; G02B 6/3584 20130101;
G02B 6/3636 20130101; B81B 3/001 20130101; G02B 6/3514 20130101;
G02B 6/3518 20130101 |
Class at
Publication: |
385/18 ;
385/17 |
International
Class: |
G02B 006/35 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2002 |
JP |
2002-135574 |
Claims
What is claimed is:
1. An optical switch manufactured by use of micromachining
technology comprising: a first substrate that comprises: a fixed
electrode substrate; and a fixed electrode that is formed on the
top surface of said fixed electrode substrate; a second substrate
that comprises: a thick single crystal silicon layer; a thin single
crystal silicon layer; and an insulation layer that is interposed
between the bottom surface of said thick single crystal silicon
layer and the top surface of said thin single crystal silicon
layer; a spacer that is interposed between the top surface of said
first substrate on which the fixed electrode is formed and the thin
single crystal silicon layer of said second substrate, and for
juxtaposing the fixed electrode of the first substrate and the thin
single crystal silicon layer of the second substrate substantially
in parallel with each other with a predetermined gap therebetween;
a movable plate-like electrode that is formed in the thin single
crystal silicon layer of the second substrate; a plurality of
flexible beam-like members for supporting the movable plate-like
electrode to be movable toward and away from the fixed electrode,
said flexible beam-like members being formed in the thin single
crystal silicon layer of the second substrate integrally with the
movable plate-like electrode; a plurality of optical fiber securing
grooves that are formed on the thick single crystal silicon layer
of the second substrate by applying an etching to the thick single
crystal silicon layer; a plurality of micro-mirrors that are formed
in a portion of the thick single crystal silicon layer of the
second substrate positioned above the movable plate-like electrode
by applying an etching to the thick single crystal silicon layer,
said micro-mirrors standing erect from the top surface of the
movable plate-like electrode through the insulation layer and being
located on the extensions of the optical fiber securing grooves;
and a through hole that is formed in the spacer and enables the
movable plate-like electrode to approach the fixed electrode, and
wherein the optical switch is constructed such that an optical path
for an optical beam incident thereon is changed by
electrostatically driving the movable plate-like electrode toward
the fixed electrode thereby to displace the micro-mirrors standing
erect from the movable plate-like electrode.
2. The optical switch as set forth in claim 1, wherein a plurality
of minute protrusions that protrude from the top surface of the
fixed electrode formed on the top surface of the fixed electrode
substrate are formed on the top surface of the fixed electrode
substrate.
3. The optical switch as set forth in claim 1 or 2; wherein the
second substrate is an SOI substrate of three layer structure that
are constituted by a thick single crystal silicon layer, a silicon
oxide layer formed on the bottom surface of said thick single
crystal silicon layer, and a thin single crystal silicon layer
joined to the bottom surface of said silicon oxide layer.
4. The optical switch as set forth in claim 1 or 2, wherein a
plurality of the micro-mirrors is four each of which has a thin
plate-like shape and one mirror surface, the four micro-mirrors
being formed on the top surface of the movable plate-like electrode
through the insulation layer by applying an chemical anisotropic
etching to the thick single crystal silicon layer in such manner
that the mirror surfaces of the micro-mirrors form at an angle of
45.degree. with the corresponding optical fiber securing grooves
and that adjacent two mirror surfaces form at right angles with
each other, and wherein a plurality of the optical fiber securing
grooves is four, and the four optical fiber securing grooves are
formed on the thick single crystal silicon layer by applying the
chemical anisotropic etching to the thick single crystal silicon
layer in such manner that two grooves are formed substantially in
parallel with each other at one side of the micro-mirrors and the
remaining two grooves are formed substantially in parallel with
each other at the other side of the micro-mirrors in the
longitudinal direction of the thick single crystal silicon layer,
the two grooves at the one side and the two grooves at the other
side being aligned with one another, and the groove surface of each
optical fiber securing groove having a generally V-shape.
5. The optical switch as set forth in claim 1 or 2, wherein a
plurality of the micro-mirrors is four each of which has a thin
plate-like shape and one mirror surface, the four micro-mirrors
being formed on the top surface of the movable plate-like electrode
through the insulation layer by applying a dry etching to the thick
single crystal silicon layer in such manner that the mirror
surfaces of the micro-mirrors form at an angle of 45.degree. with
the corresponding optical fiber securing grooves and that adjacent
two mirror surfaces form at right angles with each other, and
wherein a plurality of the optical fiber securing grooves is four,
and the four optical fiber securing grooves are formed on the thick
single crystal silicon layer by applying the dry etching to the
thick single crystal silicon layer in such manner that two grooves
are formed substantially in parallel with each other at one side of
the micro-mirrors and the remaining two grooves are formed
substantially in parallel with each other at the other side of the
micro-mirrors in the longitudinal direction of the thick single
crystal silicon layer, the two grooves at the one side and the two
grooves at the other side being aligned with one another, and the
groove surface of each optical fiber securing groove having a
generally square shape.
6. The optical switch as set forth in claim 1 or 2, wherein a
plurality of the micro-mirrors is four each of which has a thin
plate-like shape and one mirror surface, the four micro-mirrors
being formed on the top surface of the movable plate-like electrode
through the insulation layer by applying a dry etching to the thick
single crystal silicon layer in such manner that the mirror
surfaces of the micro-mirrors form at an angle of 45.degree. with
the corresponding optical fiber securing grooves and that adjacent
two mirror surfaces form at right angles with each other, and
wherein a plurality of the optical fiber securing grooves is four,
and the four optical fiber securing grooves are formed on the thick
single crystal silicon layer by applying the chemical anisotropic
etching to the thick single crystal silicon layer in such manner
that two grooves are formed substantially in parallel with each
other at one side of the micro-mirrors and the remaining two
grooves are formed substantially in parallel with each other at the
other side of the micro-mirrors in the longitudinal direction of
the thick single crystal silicon layer, the two grooves at the one
side and the two grooves at the other side being aligned with one
another, and the groove surface of each optical fiber securing
groove having a generally V-shape.
7. The optical switch as set forth in claim 1 or 2, wherein a
plurality of the micro-mirrors is two each of which has two wall
surfaces that form at right angles with each other and are used as
mirror surfaces respectively, the two micro-mirrors being formed in
opposed manner on the top surface of the movable plate-like
electrode through the insulation layer by applying a dry etching to
the thick single crystal silicon layer in such manner that the
mirror surfaces of each micro-mirror form at an angle of 45.degree.
with the corresponding optical fiber securing grooves and that
opposed mirror surfaces of the two micro-mirrors form at right
angles with each other, and wherein a plurality of the optical
fiber securing grooves is four, and the four optical fiber securing
grooves are formed on the thick single crystal silicon layer by
applying the dry etching to the thick single crystal silicon layer
in such manner that two grooves are formed substantially in
parallel with each other at one side of the micro-mirrors and the
remaining two grooves are formed substantially in parallel with
each other at the other side of the micro-mirrors in the
longitudinal direction of the thick single crystal silicon layer,
the two grooves at the one side and the two grooves at the other
side being aligned with one another, and the groove surface of each
optical fiber securing groove having a generally square shape.
8. The optical switch as set forth in claim 1 or 2, wherein a
plurality of the micro-mirrors is two each of which has two wall
surfaces that form at right angles with each other and are used as
mirror surfaces respectively, the two micro-mirrors being formed in
opposed manner on the top surface of the movable plate-like
electrode through the insulation layer by applying a dry etching to
the thick single crystal silicon layer in such manner that the
mirror surfaces of each micro-mirror form at an angle of 45.degree.
with the corresponding optical fiber securing grooves and that
opposed mirror surfaces of the two micro-mirrors form at right
angles with each other, and wherein a plurality of the optical
fiber securing grooves is four, and the four optical fiber securing
grooves are formed on the thick single crystal silicon layer by
applying the chemical anisotropic etching to the thick single
crystal silicon layer in such manner that two grooves are formed
substantially in parallel with each other at one side of the
micro-mirrors and the remaining two grooves are formed
substantially in parallel with each other at the other side of the
micro-mirrors in the longitudinal direction of the thick single
crystal silicon layer, the two grooves at the one side and the two
grooves at the other side being aligned with one another, and the
groove surface of each optical fiber securing groove having a
generally V-shape.
9. An optical switch manufactured by use of micromachining
technology comprising: a first substrate that comprises: a fixed
electrode substrate; and a fixed electrode that is formed on the
top surface of said fixed electrode substrate; a second substrate
that comprises: a thick single crystal silicon layer; a thin single
crystal silicon layer; and an insulation layer that is interposed
between the bottom surface of said thick single crystal silicon
layer and the top surface of said thin single crystal silicon
layer; a spacer that is interposed between the top surface of said
first substrate on which the fixed electrode is formed and the thin
single crystal silicon layer of said second substrate, and for
juxtaposing the fixed electrode of the first substrate and the thin
single crystal silicon layer of the second substrate substantially
in parallel with each other with a predetermined gap therebetween;
a movable plate-like electrode that is formed in the thin single
crystal silicon layer of the second substrate; a plurality of
flexible beam-like members for supporting the movable plate-like
electrode to be movable toward and away from the fixed electrode,
said flexible beam-like members being formed in the thin single
crystal silicon layer of the second substrate integrally with the
movable plate-like electrode; a plurality of optical fiber securing
grooves that are formed on the thick single crystal silicon layer
of the second substrate by applying an etching to the thick single
crystal silicon layer; a micro-mirror having a plurality of mirror
surfaces that is formed in a portion of the thick single crystal
silicon layer of the second substrate positioned above the movable
plate-like electrode by applying an etching to the thick single
crystal silicon layer, said micro-mirror standing erect from the
top surface of the movable plate-like electrode through the
insulation layer, and the mirror surfaces being located on the
extensions of the optical fiber securing grooves; and a through
hole that is formed in the spacer and enables the movable
plate-like electrode to approach the fixed electrode, and wherein
the optical switch is constructed such that an optical path for an
optical beam incident thereon is changed by electrostatically
driving the movable plate-like electrode toward the fixed electrode
thereby to displace the micro-mirror standing erect from the
movable plate-like electrode.
10. The optical switch as set forth in claim 9, wherein a plurality
of minute protrusions that protrude from the top surface of the
fixed electrode formed on the top surface of the fixed electrode
substrate are formed on the top surface of the fixed electrode
substrate.
11. The optical switch as set forth in claim 9 or 10, wherein the
second substrate is an SOI substrate of three layer structure that
are constituted by a thick single crystal silicon layer, a silicon
oxide layer formed on the bottom surface of said thick single
crystal silicon layer, and a thin single crystal silicon layer
joined to the bottom surface of said silicon oxide layer.
12. The optical switch as set forth in claim 9 or 10, wherein the
micro-mirror has a generally cross shape in plan, and a first pair
of wall surfaces of the generally cross-shaped micro-mirror forming
at right angles with each other as well as a second pair of wall
surfaces of the generally cross-shaped micro-mirror forming at
right angles with each other and opposed to the first pair of wall
surfaces are used as four mirror surfaces, the generally
cross-shaped micro-mirror being formed on the top surface of the
movable plate-like electrode through the insulation layer by
applying a dry etching to the thick single crystal silicon layer in
such manner that the four mirror surfaces form at an angle of
45.degree. with the corresponding optical fiber securing grooves,
and wherein a plurality of the optical fiber securing grooves is
four, and the four optical fiber securing grooves are formed on the
thick single crystal silicon layer by applying the dry etching to
the thick single crystal silicon layer in such manner that two
grooves are formed substantially in parallel with each other at one
side of the micro-mirrors and the remaining two grooves are formed
substantially in parallel with each other at the other side of the
micro-mirrors in the longitudinal direction of the thick single
crystal silicon layer, the two grooves at the one side and the two
grooves at the other side being aligned with one another, and the
groove surface of each optical fiber securing groove having a
generally square shape.
13. The optical switch as set forth in claim 9 or 10, wherein the
micro-mirror has a generally cross shape in plan, and a first pair
of wall surfaces of the generally cross-shaped micro-mirror forming
at right angles with each other as well as a second pair of wall
surfaces of the generally cross-shaped micro-mirror forming at
right angles with each other and opposed to the first pair of wall
surfaces are used as four mirror surfaces, the generally
cross-shaped micro-mirror being formed on the top surface of the
movable plate-like electrode through the insulation layer by
applying a dry etching to the thick single crystal silicon layer in
such manner that the four mirror surfaces form at an angle of
45.degree. with the corresponding optical fiber securing grooves,
and wherein a plurality of the optical fiber securing grooves is
four, and the four optical fiber securing grooves are formed on the
thick single crystal silicon layer by applying the chemical
anisotropic etching to the thick single crystal silicon layer in
such manner that two grooves are formed substantially in parallel
with each other at one side of the micro-mirrors and the remaining
two grooves are formed substantially in parallel with each other at
the other side of the micro-mirrors in the longitudinal direction
of the thick single crystal silicon layer, the two grooves at the
one side and the two grooves at the other side being aligned with
one another, and the groove surface of each optical fiber securing
groove having a generally V-shape.
14. The optical switch as set forth in claim 12, wherein the
micro-mirror having a generally cross shape in plan is one having a
modified cross shape in plan in which the central portion thereof
including the crossing is formed into a pillar the area of section
of which is larger.
15. The optical switch as set forth in claim 13, wherein the
micro-mirror having a generally cross shape in plan is one having a
modified cross shape in plan in which the central portion thereof
including the crossing is formed into a pillar the area of section
of which is larger.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical switch that is
manufactured by use of micromachining technology and used in
changing the optical path of an optical signal, and more
particularly, to an optical switch configured such that the
electrode-to-electrode distance between a movable plate-like
electrode and a fixed or stationary electrode of the optical switch
can be easily set to a desired distance.
[0003] 2. Description of the Related Art
[0004] Optical switches of various types that are manufactured by
use of micromachining technology have been heretofore provided. For
example, an example of the prior art 2.times.2 optical switch will
be described with reference to FIGS. 1 and 2. In the specification,
the 2.times.2 optical switch is defined such that it has two input
side optical fibers mounted thereto each emitting an optical signal
therefrom and two output side optical fibers mounted thereto each
receiving an optical signal incident thereon and that is capable of
concurrently switching the optical paths of optical signals emitted
respectively from the two output side optical fibers so that each
optical signal is incident on corresponding one of the two input
side optical fibers.
[0005] FIG. 1 is a plan view illustrating a construction of the
prior art 2.times.2 optical switch, and FIG. 2 is a generally
sectional view taken along the line 2-2 in FIG. 1 and looking in
the direction indicated by the arrows. The illustrated optical
switch SW1 comprises: a movable electrode supporting plate 14 of a
generally rectangle in plan; an opening 13 of a generally square in
plan formed in the movable electrode supporting plate 14 at
generally the central portion thereof; four V-shaped grooves 25A,
26A and 25B, 26B, two grooves 25A and 26A of which are formed on
the top surface of the movable electrode supporting plate 14 in the
longitudinal direction thereof at one side of the opening 13 and
the remaining two grooves 25B and 26B of which are formed on the
top surface of the movable electrode supporting plate 14 in the
longitudinal direction thereof at the opposite side of the opening
13; a fixed or stationary electrode substrate 19 of a generally
rectangle in plan and of a substantially the same shape and size as
those of the movable electrode supporting plate 14, the fixed
electrode substrate 19 being disposed underneath the movable
electrode supporting plate 14 and having its elevated portion 18 on
the center thereof to be fitted into the opening 13 of the movable
electrode supporting plate 14; a movable plate-like electrode 11 of
a generally square in plan that is disposed substantially in
parallel with the elevated portion 18 of the fixed electrode
substrate 19 with a predetermined space or gap between them and
above the opening 13 of the movable electrode supporting plate 14;
four flexible beams 12A1, 12A2, 12B1, and 12B2 for supporting the
movable plate-like electrode 11 to be movable toward and away from
the elevated portion 18 of the fixed electrode substrate 19; and
four thin plate-like or sheet-like micro-mirrors 17A1, 17A2, 17B1,
and 17B2 upstanding from the top surface of the movable plate-like
electrode 11.
[0006] Each of the four flexible beams 12A1, 12A2, 12B1, and 12B2
is called "flexure" in this technical field, and the base of each
of the two beams 12A1 and 12A2 is integrally connected to
corresponding one of the two opposed ends of one anchor portion 15A
of a generally rectangle in plan in the longitudinal direction
thereof, the anchor portion 15A being opposed to the other anchor
portion 15B of a generally rectangle in plan. The base of each of
the remaining two beams 12B1 and 12B2 thereof is integrally
connected to corresponding one of the two opposed ends of the other
anchor portion 15B of a generally rectangle in plan in the
longitudinal direction thereof. Each of the four beams 12A1, 12A2
and 12B1, 12B2 extends from corresponding one of the two opposed
ends of each of the anchor portions 15A and 15B along corresponding
one of the four sides of the movable plate-like electrode 11, and
each of the four ends thereof is integrally connected to
corresponding one of the four corners of the movable plate-like
electrode 11. The paired anchor portions 15A and 15B are fixed to
the movable electrode supporting plate 14 at the both sides of the
opening 13 in the longitudinal direction of the movable electrode
supporting plate 14.
[0007] Each of the four V-shaped grooves 25A, 26A and 25B, 26B
extends from a predetermined position outside the pair of anchor
portions 15A and 15B (a predetermined position toward the ends of
the movable electrode supporting plate 14 in the longitudinal
direction thereof) to corresponding one of the ends of the movable
electrode supporting plate 14 in the longitudinal direction
thereof, and the two V-shaped grooves 25A and 26A and the two
V-shaped grooves 25B and 26B opposed to one another through the
opening 13 put therebetween in the longitudinal direction of the
movable electrode supporting plate 14 are aligned with one
another.
[0008] The four thin plate-like micro-mirrors 17A1, 17A2, 17B1 and
17B2 have substantially the same shape and size with one another,
and the two micro-mirrors 17A1 and 17B1 are disposed on a first
straight line that passes through substantially the center of the
movable plate-like electrode 11 and forms an angle of 45.degree.
with a horizontal line. The remaining two micro-mirrors 17A2 and
17B2 are disposed on a second straight line that passes through
substantially the center of the movable plate-like electrode 11 and
is orthogonal to the first straight line. These micro-mirrors 17A1,
17A2, 17B1 and 17B2 are disposed at such positions that they are
away by substantially the same distance in the radial direction
from the intersection between the first and second straight lines
and that axial lines of corresponding two V-shaped grooves 25A and
26B and of corresponding two V-shaped grooves 26A and 25B pass
through substantially the centers of the micro-mirrors.
[0009] The micro-mirrors 17A1, 17A2, 17B1, 17B2 may be fabricated,
for example, by applying a photoresist film of a predetermined
thickness on the top surface of the movable plate-like electrode
11, exposing only portions of the photoresist film on which the
micro-mirrors are to be formed, thereafter removing the photoresist
film except for the exposed portions thereof by use of a solvent to
form four micro-mirror bodies, and coating mirror surfaces of these
micro-mirror bodies with a metal such as gold (Au) or the like.
[0010] Alternatively, as described in Japanese Patent Application
No. 243582/2001 (or PCT Application PCT/JP02/08177 filed on Aug. 9,
2002 claiming a priority of Japanese Patent Application No.
243582/2001) filed on Aug. 10, 2001 by the same assignee as that of
the present application, micro-mirrors erecting from a silicon
substrate may be fabricated by applying an orientation-dependent
wet etching or chemical anisotropic wet etching to the silicon
substrate the surface of which is (100) crystal face. In such case,
since the mirror surface of each micro-mirror becomes (100) crystal
face, the accuracy in verticality and flatness of each micro-mirror
comes to much high, and hence optical loss can be minimized.
Further, the details thereof will be referred to the above Japanese
Patent Application No. 243582/2001 (or PCT/JP02/08177), or a paper
entitled "SELF ALIGNED VERTICAL MIRRORS AND V-GROOVES APPLIED TO A
SELF-LATCHING MATRIX SWITCH FOR OPTICAL NETWORKS" published by
Philippe Helin, et al. in Thirteenth IEEE International Micro
Electro Mechanical Systems Conference (MEMS-2000) held on Jan. 23
through 27, 2000 at Miyazaki, Japan.
[0011] Optical fibers are located and mounted in the four V-shaped
grooves 25A, 26A and 25B, 26B, respectively. In this example, an
output side optical fiber 31A and an input side optical fiber 32A
are located and mounted in the V-shaped grooves 25A and 26A
positioned in the left side in FIG. 1, respectively, and in the
V-shaped grooves 25B and 26B positioned in the right side in FIG. 1
are located and mounted an output side optical fiber 31B and an
input side optical fiber 32B, respectively. As a result, the output
side optical fiber 31A mounted in the V-shaped groove 25A and the
input side optical fiber 32A mounted in the V-shaped groove 26B are
opposed to and aligned to each other (are disposed on the same
optical axis line), and the input side optical fiber 32A mounted in
the V-shaped groove 26A and the output side optical fiber 31B
mounted in the V-shaped grooves 25B are opposed to and aligned to
each other (are disposed on the same optical axis line).
[0012] The movable electrode supporting plate 14, four beams 12A1,
12A2, 12B1 and 12B2, the pair of anchor portions 15A and 15B, and
movable plate-like electrode 11 can be formed into one body. For
example, a substrate made of single crystal silicon of a
predetermined thickness is used as the movable electrode supporting
plate 14, and an insulation layer, for example, silicon dioxide
(SiO.sub.2) layer 21 is formed on the top surface of the single
crystal silicon substrate 14, and on the top surface of the silicon
dioxide layer 21 is formed, for example, a single crystal silicon
layer. The single crystal silicon layer is processed using
photolithography technology to form the above-mentioned four beams
12A1, 12A2, 12B1 and 12B2, the pair of anchor portions 15A and 15B,
and movable plate-like electrode 11 therefrom. Thereafter, the
single crystal silicon substrate 14 is etched from the bottom
surface side thereof to form the opening 13 of a generally square
therein. Thus, the four beams 12A1, 12A2, 12B1 and 12B2, the pair
of anchor portions 15A and 15B, and movable plate-like electrode 11
are formed into one body as well as the pair of anchor portions 15A
and 15B is integrally fixed to the top surface of the movable
electrode supporting plate 14. Further, in FIG. 2, a reference
numeral 22 denotes an insulation layer (for example, silicon
dioxide layer) that is previously formed on the bottom surface of
the movable electrode supporting plate 14. This insulation layer 22
is used as a mask in forming the opening 13 in the movable
electrode supporting plate 14 by use of photolithography
technology.
[0013] In general, an SOI (Silicon on Insulator) substrate of a
generally rectangle in plan will be used to form the movable
electrode supporting plate 14, four beams 12A1, 12A2, 12B1 and
12B2, the pair of anchor portions 15A and 15B, and movable
plate-like electrode 11 that are united with one another by use of
photolithography technology. Since such manufacturing method for an
optical switch is well known, it will be described in brief, here.
Further, a 2.times.2 optical switch having the same construction as
that of the above-mentioned 2.times.2 optical switch has been
described in, for example, Japanese Patent Application Public
Disclosure No. 82292/2002 (Japanese Patent Application No.
270621/2000), and therefore, the details thereof including the
manufacturing method will be referred to this Japanese Patent
Application Public Disclosure No. 82292/2002 (P2002-82292A).
[0014] First, an SOI substrate of a generally rectangle in plan is
prepared. Generally, the SOI substrate is constituted by three
layers that are a thick support substrate made of single crystal
silicon, an insulation layer on the top of the thick support
substrate, and a thin layer of single crystal silicon on the top of
the insulation layer. In this example, there is used an SOI
substrate comprising a thick support substrate (not shown in FIGS.
1 and 2) of single crystal silicon of a generally rectangle in
plan, an insulation layer 21 of silicon dioxide formed on the top
surface of the support substrate, and a thin layer (not shown in
FIGS. 1 and 2) of single crystal silicon joined onto the top
surface of the silicon dioxide layer 21. However, it goes without
saying that any SOI substrate manufactured by use of one of known
other methods or processes may be used. Further, in this example,
the insulation layer (for example, silicon dioxide layer) 22 is
previously formed on the bottom surface of the SOI substrate.
[0015] Next, by use of photolithography technology, a patterning of
the thin single crystal silicon layer of the SOI substrate is done
to leave portions thereof corresponding to shapes of the four beams
12A1, 12A2, 12B1 and 12B2, the pair of anchor portions 15A and 15B,
and movable plate-like electrode 11 so that the thin single crystal
silicon layer is removed except for the portions thereof
corresponding to shapes of the four beams, the pair of anchor
portions, and movable plate-like electrode. Thereafter, a portion
of the silicon dioxide layer 22 on the bottom surface of the SOI
substrate, which corresponds to the opening 13 of the movable
electrode supporting plate 14, is removed. Thus, the four beams
12A1, 12A2, 12B1 and 12B2, the pair of anchor portions 15A and
151B, and movable plate-like electrode 11 are formed into one body
from the thin single crystal silicon layer on the silicon dioxide
layer 21 of the SOI substrate.
[0016] Next, the support substrate of single crystal silicon is
etched from the bottom surface side of the SOI substrate using KOH
solution to form the opening 13. As a result, the movable electrode
supporting plate 14 of a generally rectangle in plan is formed from
the support substrate of single crystal silicon of a generally
rectangle in plan.
[0017] Further, it is needless to say that the opening 13 of a
generally square formed in the movable electrode supporting plate
14 has such a size that it can accommodate the movable plate-like
electrode 11 and four beams 12A1, 12A2, 12B1 and 12B2 therein.
[0018] The fixed electrode substrate 19 is a substrate made of, for
example, single crystal silicon of a generally rectangle in plan,
and at the central portion of the top surface thereof is formed the
above-mentioned elevated portion 18 having substantially the same
shape (in this example, generally square) and size as those of the
opening 13 formed through the movable electrode supporting plate
14. The movable electrode supporting plate 14 constructed as
discussed above is put on the fixed electrode substrate 19, and
then, they are united by using, for example, a suitable adhesive or
bonding agent. When the movable electrode supporting plate 14 is
put on the fixed electrode substrate 19, the elevated portion 18 of
the fixed electrode substrate 19, which serves as a fixed electrode
fits into the opening 13 of the movable electrode supporting plate
14 from the bottom side thereof so that the elevated portion 18 of
the fixed electrode substrate 19 and the movable plate-like
electrode 11 are mounted in opposed state to each other with a
predetermined space or gap therebetween. In such manner, the
optical switch SW1 shown in FIGS. 1 and 2 is constructed. Further,
in FIG. 2, a reference numeral 28 denotes an insulation layer
(silicon dioxide layer) that is used as a mask in forming the
elevated portion 18 on the fixed electrode substrate 19. This
insulation layer 28 prevents the movable plate-like electrode 11
from being electrically connected to the elevated portion 18 of the
fixed electrode substrate 19 when the movable plate-like electrode
11 is driven toward the elevated portion 18 and comes into contact
with the top surface of the elevated portion 18.
[0019] According to the optical switch SW1 constructed as discussed
above, the movable plate-like electrode 11 is allowed to move into
the opening 13, and if a predetermined drive voltage is applied
between the fixed electrode substrate 19 and the movable plate-like
electrode 11 to produce an electrostatic attraction therebetween in
such direction that the movable plate-like electrode 11 and the
fixed electrode substrate 19 are attracted to each other, the
movable plate-like electrode 11 is downwardly displaced, and hence
the micro-mirrors 17A1, 17A2, 17B1 and 17B2 formed on and
upstanding from the top surface of the movable plate-like electrode
11 are also displaced downwardly to a position where the
micro-mirrors are out of the optical paths through each of which an
optical signal (beam) will propagate.
[0020] Specifically explaining, in case any drive voltage is not
applied between the fixed electrode substrate 19 and the movable
plate-like electrode 11 so that the movable plate-like electrode 11
is not displaced and hence the micro-mirrors on the top surface of
the movable plate-like electrode 11 exist on the optical paths
through which optical signals (beams) emitted respectively from the
output side optical fibers 31A and 31B will propagate, the optical
signal (beam) emitted from the output side optical fiber 31A is
reflected by the micro-mirror 17A1 existing on the optical path for
that optical signal in the direction of forming an angle of
90.degree. (forming a right angle) with the incident beam, and is
incident on the micro-mirror 17A2. The incident optical signal is
further reflected by the micro-mirror 17A2 in the direction of
forming an angle of 90.degree., and is incident on the input side
optical fiber 32A. Likewise, the optical signal (beam) emitted from
the output side optical fiber 31B is reflected by the micro-mirror
17B1 existing on the optical path for that optical signal in the
direction of forming a right angle with the incident beam, and is
incident on the micro-mirror 17B2. The incident optical signal is
further reflected by the micro-mirror 17B2 in the direction of
forming an angle of 90.degree., and is incident on the input side
optical fiber 32B.
[0021] On the contrary, in case a predetermined drive voltage is
applied between the fixed electrode substrate 19 and the movable
plate-like electrode 11 so that the movable plate-like electrode 11
is electrostatically driven toward the fixed electrode substrate 19
and hence the micro-mirrors on the top surface of the movable
plate-like electrode 11 are moved downwardly so that they do not
exist on (they are out of) the optical paths through which optical
signals (beams) emitted respectively from the output side optical
fibers 31A and 31B will propagate, the optical signal emitted from
the output side optical fiber 31A goes right on without being
reflected by the micro-mirrors 17A1 and 17B2, and is incident on
the input side optical fiber 32B that is opposed to the output side
optical fiber 31A. Likewise, the optical signal emitted from the
output side optical fiber 31B goes right on without being reflected
by the micro-mirrors 17B1 and 17A2, and is incident on the input
side optical fiber 32A that is opposed to the output side optical
fiber 31B. Thus, the optical path for the optical signal emitted
from the output side optical fiber 31A can be switched from the
input side optical fiber 32A to the input side optical fiber 32B,
and similarly, the optical path for the optical signal emitted from
the output side optical fiber 31B can be switched from the input
side optical fiber 32B to the input side optical fiber 32A. In
other words, the optical switch SW1 constructed as described above
is capable of switching in space the optical path of an optical
signal propagating through an optical waveguide or optical
transmission line (path) without any intervention of a solid state
optical waveguide.
[0022] In an optical switch of this type, in general, it is
desirable in circuit design to make it possible that the movable
plate-like electrode 11 is driven toward the stationary electrode
substrate 19 by application of a drive voltage as low as possible.
In other words, it is desirable in circuit design to reduce the
absolute value of a drive voltage for driving the movable
plate-like electrode 11 toward the stationary electrode substrate
19 to a value as small as possible. For such reason, in the prior
art optical switch SW1 constructed as discussed above, the movable
plate-like electrode 11, the four beams 12A1, 12A2, 12B1, 12B2, and
the anchor portions 15A, 15B are formed into one body, and yet, the
thickness of the movable plate-like electrode 11 and the four beams
12A1, 12A2, 12B1, 12B2 is made thin to lighten the weight thereof
and to lessen the elastic forces of the four beams. However, the
four beams must have their elastic forces for holding the movable
plate-like electrode 11 substantially in parallel with the fixed
electrode substrate 19 and for returning the movable plate-like
electrode 11 already attracted to the fixed electrode substrate 19
to its original position therefrom. Therefore, there is a limit in
reducing the magnitude of the drive voltage that is required to
drive the movable plate-like electrode 11 by the predetermined
distance toward the fixed electrode substrate 19.
[0023] In addition, in the above-constructed optical switch SW1,
there is proposed another method for reducing the absolute value of
a drive voltage in which the electrode-to-electrode distance (gap)
between the movable plate-like electrode 11 and the fixed electrode
substrate 19 is set to a necessary and minimum length. In such
case, the thickness of the movable electrode supporting plate 14
(in case of using an SOI substrate, the support substrate of single
crystal silicon) cannot be made thin too much in view of
manufacturing process, and accordingly, there is adopted a
procedure that the electrode-to-electrode distance between the
movable plate-like electrode 11 and the fixed electrode substrate
19 is set to a necessary and minimum distance by providing the
elevated portion 18 on the surface of the fixed electrode substrate
19 as shown in FIG. 2.
[0024] In this manner, in case the electrode-to-electrode distance
is set to a necessary and minimum distance, the movable plate-like
electrode 11 is electrostatically driven toward the fixed electrode
substrate 19 until it comes into contact with the top surface of
the elevated portion 18.
[0025] The relationship between the drive voltage to be applied to
the movable plate-like electrode 11 and the distance that the
movable plate-like electrode 11 is to be driven is not linear. It
is characterized in that when the drive voltage applied to the
movable plate-like electrode 11 is gradually increased, the movable
plate-like electrode 11 is driven downwardly toward the fixed
electrode substrate 19, and that when the driven distance of the
movable plate-like electrode 11 becomes equal to or more than 1/3
of the electrode-to-electrode distance X between the bottom surface
of the movable plate-like electrode 11 and the top surface of the
elevated portion 18 of the fixed electrode substrate 19, the
movable plate-like electrode 11 is driven at a dash toward the
fixed electrode substrate 19 and is attracted or stuck to the top
surface of the fixed electrode substrate 19 (in practice, the top
surface of the elevated portion 18). A drive voltage by which the
movable plate-like electrode 11 is driven at a dash toward the
fixed electrode substrate 19 is called "pull-in voltage" in this
technical field. Further, the details of the pull-in voltage will
be referred to Japanese Patent Application Nos. 75443/2002
(P2002-75443) and 75817/2002 (P2002-75817) both of which were filed
on Mar. 19, 2002, by the same assignee as that of the present
application, or the homepage of Professor Hiroshi TOSHIYOSHI,
Institute of Industrial Science, University of Tokyo:
[0026]
http://toshi.fujita3.iis.u-tokyo.ac.jp/onlinelecture/electrostatic1-
.pdf
[0027] In the prior art, since the movable plate-like electrode 11
is driven until it comes into contact with the top surface of the
elevated portion 18 of the fixed electrode substrate 19 (by the
distance X), the drive voltage is necessarily set to a voltage
equal to or higher than the pull-in voltage. For this reason, when
the movable plate-like electrode 11 moves over the distance equal
to 1/3 of the electrode-to-electrode distance X, it is driven at a
dash toward the fixed electrode substrate 19 thereby to come into
contact with the top surface of the elevated portion 18 of the
fixed electrode substrate 19.
[0028] When the movable plate-like electrode 11 is displaced
downwardly and the bottom surface thereof comes into contact with
the top surface of the elevated portion 18 of the fixed electrode
substrate 19, a phenomenon occurs that van der Waals' force acts or
affects between the bottom surface of the movable plate-like
electrode 11 and the top surface of the elevated portion 18 of the
fixed electrode substrate 19 so that they are attracted to each
other, and that the movable plate-like electrode 11 is not restored
to its original position in an instant even the application of the
drive voltage is stopped. That is, there occurs a phenomenon that
the movable plate-like electrode 11 and the elevated portion 18 of
the fixed electrode substrate 19 are temporarily or permanently
attracted or stuck to each other by van der Waals' force. This
phenomenon is called "sticking" in this technical field.
Consequently, it is impossible to switch the path of an optical
signal at once, and hence there is a disadvantage that the
reliability of switching operation is greatly deteriorated.
[0029] In view of the foregoing, there is proposed an optical
switch that is constructed such that minute protrusions are formed
on either one of the bottom surface of the movable plate-like
electrode 11 opposed to the fixed electrode substrate 19 or the top
surface of the fixed electrode substrate 19 opposed to the movable
plate-like electrode 11 to reduce the contact area between the
movable plate-like electrode 11 and the fixed electrode substrate
19, or a second fixed electrode pattern for preventing the sticking
from occurring is formed on the top surface of the fixed electrode
substrate 19, thereby to prevent occurrence of the phenomenon that
the movable plate-like electrode 11 and the fixed electrode
substrate 19 are temporarily or permanently attracted to each other
by van der Waals' force. Such optical switch is disclosed in, for
example, Japanese Patent Application Public Disclosure No.
256563/1998, Japanese Patent Application Public Disclosure No.
264650/2001 (P2001-264650A), or Japanese Patent Application Public
Disclosure No. 39392/2003 (P2003-39392A).
[0030] There is shown in FIG. 3 an example of the prior art optical
switch in which a plurality of minute protrusions are formed on the
top surface of the elevated portion 18 of the fixed electrode
substrate 19 to reduce the contact area between the movable
plate-like electrode 11 and the elevated portion 18 of the fixed
electrode substrate 19. FIG. 3 is a sectional view similar to FIG.
2, and the optical switch SW2 shown in FIG. 3 may have the same
construction, structure and shape as those of the prior art optical
switch SW1 already discussed with reference to FIGS. 1 and 2 except
that a plurality of minute protrusions 23 are formed, for example,
in a matrix manner on the top surface of the elevated portion 18 of
the fixed electrode substrate 19. Therefore, in FIG. 3, portions
and elements corresponding to those shown in FIGS. 1 and 2 will be
denoted by the same reference characters attached thereto and
explanation thereof will be omitted unless necessary.
[0031] In case a plurality of minute or very small protrusions 23
are formed, for example, in a matrix manner on the top surface of
the elevated portion 18 of the fixed electrode substrate 19, when
the movable plate-like electrode 11 is electrostatically driven
downwardly and comes into contact with the top surface of the
elevated portion 18 of the fixed electrode substrate 19, the bottom
surface of the movable plate-like electrode 11 comes into contact
with the pointed ends of these protrusions 23, and hence the
movable plate-like electrode 11 is not in surface contact with the
elevated portion 18 of the fixed electrode substrate 19.
Accordingly, it is possible to greatly decrease the contact area
between them and to prevent the sticking from occurring.
[0032] However, in order to prevent the movable plate-like
electrode 11 from being electrically connected to the elevated
portion 18 of the fixed electrode substrate 19 when the movable
plate-like electrode 11 is driven toward the fixed electrode
substrate 19 and comes into contact with the elevated portion 18
thereof, the protrusions 23 must be made of an insulation material
or the surfaces of the protrusions 23 must be covered or coated
with an insulation material. In case of forming the plural
protrusions 23 on the top surface of the elevated portion 18 of the
fixed electrode substrate 19, in general, a photoresist is applied
on the top surface of the oxide film (oxide film, usually, silicon
dioxide layer, used as a mask when the elevated portion 18 is
formed) on the elevated portion 18, and the oxide film is patterned
in a pattern corresponding to the protrusions 23, and then, the
elevated portion 18 is etched using the patterned oxide film as a
mask. Thus, the plural protrusions 23 are formed on the top surface
of the elevated portion 18. For example, in case a plurality of the
fixed electrode substrates 19 each having such elevated portion 18
formed thereon are arranged on a wafer or chip, even if a
photoresist is dropped on the top surface of each of the elevated
portions 18 and is coated thereon by spinning the wafer, it is
impossible to spread the photoresist on the top surface of each
elevated portion 18 with uniform thickness and satisfaction.
Accordingly, there is a drawback that it is much difficult to form
the protrusions 23 with high precision that have been accurately
located at desired positions and have uniform height. In other
words, in case the fixed electrode substrate 19 has its elevated
portion 18 formed on the top surface thereof, it is much difficult
to form on the top surface of the elevated portion 18 a plurality
of the very small protrusions 23 with high precision that have been
accurately located at desired positions and have uniform height.
Further, in FIG. 3, a reference character 29 denotes an insulation
layer (oxide film) formed on the top surface of the elevated
portion 18. In addition, the details of a method of manufacturing a
plurality of protrusions will be referred to the above-mentioned
Japanese Patent Application Public Disclosure No. 256563/1998,
Japanese Patent Application Public Disclosure No. 264650/2001
(P2001-264650A), or Japanese Patent Application Public Disclosure
No. 39392/2003 (P2003-39392A).
SUMMARY OF THE INVENTION
[0033] It is an object of the present invention to provide an
optical switch that is configured such that the
electrode-to-electrode distance between the movable plate-like
electrode and the fixed electrode of the optical switch can be
easily set to a desired distance.
[0034] It is another object of the present invention to provide an
optical switch in which a plurality of protrusions or an electrode
pattern for preventing the sticking from occurring can easily be
formed on the surface of the fixed electrode substrate of the
optical switch with high accuracy.
[0035] In order to accomplish the above objects, in an aspect of
the present invention, there is provided an optical switch
manufactured by use of micromachining technology, which comprises:
a first substrate comprising: a fixed electrode substrate; and a
fixed electrode that is formed on the top surface of the fixed
electrode substrate; a second substrate comprising: a thick single
crystal silicon layer; a thin single crystal silicon layer; and an
insulation layer that is interposed between the bottom surface of
the thick single crystal silicon layer and the top surface of the
thin single crystal silicon layer; a spacer that is interposed
between the top surface of the first substrate on which the fixed
electrode is formed and the thin single crystal silicon layer of
the second substrate, and for juxtaposing the fixed electrode of
the first substrate and the thin single crystal silicon layer of
the second substrate substantially in parallel with each other with
a predetermined gap therebetween; a movable plate-like electrode
that is formed in the thin single crystal silicon layer of the
second substrate; a plurality of flexible beam-like members for
supporting the movable plate-like electrode to be movable toward
and away from the fixed electrode, the flexible beam-like members
being formed in the thin single crystal silicon layer of the second
substrate integrally with the movable plate-like electrode; a
plurality of optical fiber securing grooves that are formed on the
thick single crystal silicon layer of the second substrate by
applying an etching to the thick single crystal silicon layer; a
plurality of micro-mirrors that are formed in a portion of the
thick single crystal silicon layer of the second substrate
positioned above the movable plate-like electrode by applying an
etching to the thick single crystal silicon layer, the
micro-mirrors standing erect from the top surface of the movable
plate-like electrode through the insulation layer and being located
on the extensions of the optical fiber securing grooves; and a
through hole that is formed in the spacer and enables the movable
plate-like electrode to approach the fixed electrode, and wherein
the optical switch is constructed such that an optical path for an
optical beam incident thereon is changed by electrostatically
driving the movable plate-like electrode toward the fixed electrode
thereby to displace the micro-mirrors standing erect from the
movable plate-like electrode.
[0036] In a first preferred embodiment, a plurality of the
micro-mirrors is four each of which has a thin plate-like shape and
one mirror surface, and the four micro-mirrors are formed on the
top surface of the movable plate-like electrode through the
insulation layer by applying an chemical anisotropic etching to the
thick single crystal silicon layer in such manner that the mirror
surfaces of the micro-mirrors form at an angle of 45.degree. with
the corresponding optical fiber securing grooves and that adjacent
two mirror surfaces form at right angles with each other. A
plurality of the optical fiber securing grooves is four, and the
four optical fiber securing grooves are formed on the thick single
crystal silicon layer by applying the chemical anisotropic etching
to the thick single crystal silicon layer in such manner that two
grooves are formed substantially in parallel with each other at one
side of the micro-mirrors and the remaining two grooves are formed
substantially in parallel with each other at the other side of the
micro-mirrors in the longitudinal direction of the thick single
crystal silicon layer, the two grooves at the one side and the two
grooves at the other side being aligned with one another, and the
groove surface of each optical fiber securing groove having a
generally V-shape.
[0037] The four micro-mirrors as well as the four optical fiber
securing grooves may be formed by applying a dry etching to the
thick single crystal silicon layer. In such case, the groove
surface of each optical fiber securing groove has a generally
square shape.
[0038] Alternatively, the four micro-mirrors may be formed by
applying a dry etching to the thick single crystal silicon layer,
and the four optical fiber securing grooves may be formed by
applying the chemical anisotropic etching to the thick single
crystal silicon layer.
[0039] Alternatively, two micro-mirrors each of which has two wall
surfaces forming at right angles with each other and are used as
mirror surfaces respectively, may be formed in opposed manner on
the top surface of the movable plate-like electrode through the
insulation layer by applying a dry etching to the thick single
crystal silicon layer in such manner that the mirror surfaces of
each micro-mirror form at an angle of 45.degree. with the
corresponding optical fiber securing grooves and that opposed
mirror surfaces of the two micro-mirrors form at right angles with
each other. In such case, the four optical fiber securing grooves
may be formed by applying either of a dry etching or an chemical
anisotropic etching to the thick single crystal silicon layer.
[0040] In another aspect of the present invention, there is
provided an optical switch manufactured by use of micromachining
technology, which comprises: a first substrate comprising: a fixed
electrode substrate; and a fixed electrode that is formed on the
top surface of the fixed electrode substrate; a second substrate
comprising: a thick single crystal silicon layer; a thin single
crystal silicon layer; and an insulation layer that is interposed
between the bottom surface of the thick single crystal silicon
layer and the top surface of the thin single crystal silicon layer;
a spacer that is interposed between the top surface of the first
substrate on which the fixed electrode is formed and the thin
single crystal silicon layer of the second substrate, and for
juxtaposing the fixed electrode of the first substrate and the thin
single crystal silicon layer of the second substrate substantially
in parallel with each other with a predetermined gap therebetween;
a movable plate-like electrode that is formed in the thin single
crystal silicon layer of the second substrate; a plurality of
flexible beam-like members for supporting the movable plate-like
electrode to be movable toward and away from the fixed electrode,
the flexible beam-like members being formed in the thin single
crystal silicon layer of the second substrate integrally with the
movable plate-like electrode; a plurality of optical fiber securing
grooves that are formed on the thick single crystal silicon layer
of the second substrate by applying an etching to the thick single
crystal silicon layer; a micro-mirror having a plurality of mirror
surfaces that is formed in a portion of the thick single crystal
silicon layer of the second substrate positioned above the movable
plate-like electrode by applying an etching to the thick single
crystal silicon layer, the micro-mirror standing erect from the top
surface of the movable plate-like electrode through the insulation
layer, and the mirror surfaces being located on the extensions of
the optical fiber securing grooves; and a through hole that is
formed in the spacer and enables the movable plate-like electrode
to approach the fixed electrode, and wherein the optical switch is
constructed such that an optical path for an optical beam incident
thereon is changed by electrostatically driving the movable
plate-like electrode toward the fixed electrode thereby to displace
the micro-mirror standing erect from the movable plate-like
electrode.
[0041] In a second preferred embodiment, the micro-mirror has a
generally cross shape in plan, and a first pair of wall surfaces of
the generally cross-shaped micro-mirror forming at right angles
with each other as well as a second pair of wall surfaces of the
generally cross-shaped micro-mirror forming at right angles with
each other and opposed to the first pair of wall surfaces are used
as four mirror surfaces, the generally cross-shaped micro-mirror
being formed on the top surface of the movable plate-like electrode
through the insulation layer by applying a dry etching to the thick
single crystal silicon layer in such manner that the four mirror
surfaces form at an angle of 45.degree. with the corresponding
optical fiber securing grooves. A plurality of the optical fiber
securing grooves is four, and the four optical fiber securing
grooves are formed on the thick single crystal silicon layer by
applying the dry etching to the thick single crystal silicon layer
in such manner that two grooves are formed substantially in
parallel with each other at one side of the micro-mirrors and the
remaining two grooves are formed substantially in parallel with
each other at the other side of the micro-mirrors in the
longitudinal direction of the thick single crystal silicon layer,
the two grooves at the one side and the two grooves at the other
side being aligned with one another, and the groove surface of each
optical fiber securing groove having a generally square shape.
[0042] In addition, the central portion including the crossing of
the micro-mirror having a generally cross shape in plan is formed
into a pillar the area of section of which is larger.
[0043] In a third preferred embodiment, the micro-mirror has a
generally cross shape in plan, and a first pair of wall surfaces of
the generally cross-shaped micro-mirror forming at right angles
with each other as well as a second pair of wall surfaces of the
generally cross-shaped micro-mirror forming at right angles with
each other and opposed to the first pair of wall surfaces are used
as four mirror surfaces, the generally cross-shaped micro-mirror
being formed on the top surface of the movable plate-like electrode
through the insulation layer by applying a dry etching to the thick
single crystal silicon layer in such manner that the four mirror
surfaces form at an angle of 45.degree. with the corresponding
optical fiber securing grooves. A plurality of the optical fiber
securing grooves is four, and the four optical fiber securing
grooves are formed on the thick single crystal silicon layer by
applying an chemical anisotropic etching to the thick single
crystal silicon layer in such manner that two grooves are formed
substantially in parallel with each other at one side of the
micro-mirrors and the remaining two grooves are formed
substantially in parallel with each other at the other side of the
micro-mirrors in the longitudinal direction of the thick single
crystal silicon layer, the two grooves at the one side and the two
grooves at the other side being aligned with one another, and the
groove surface of each optical fiber securing groove having a
generally V-shape.
[0044] In each of the embodiments, a plurality of minute
protrusions that protrude from the top surface of the fixed
electrode formed on the top surface of the fixed electrode
substrate may be formed on the top surface of the fixed electrode
substrate in order to prevent the sticking from occurring.
[0045] In addition, an SOI substrate of three layer structure that
are constituted by a thick single crystal silicon layer, a silicon
oxide layer formed on the bottom surface of the thick single
crystal silicon layer, and a thin single crystal silicon layer
joined to the bottom surface of the silicon oxide layer may be used
as the second substrate.
[0046] With the construction as described above, by selecting the
thickness of the spacer that is easy in manufacture, the
electrode-to-electrode distance (gap) between the movable
plate-like electrode and the fixed electrode can be easily set to a
desired distance. Therefore, it is easy to set the
electrode-to-electrode distance to a necessary and minimum
distance. In addition, since there is no need to provide an
elevated portion on the fixed electrode substrate unlike the prior
art optical switches, the surface of the fixed electrode substrate
on which the fixed electrode is to be formed is flat. Consequently,
an electrode pattern for preventing the sticking from occurring or
the like can easily be formed on the surface of the fixed electrode
substrate with high accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a plan view showing an example of the prior art
optical switch;
[0048] FIG. 2 is a sectional view taken along the line 2-2 in FIG.
1 and looking in the direction indicated by the arrows;
[0049] FIG. 3 is a sectional view similar to FIG. 2 showing another
example of the prior art optical switch;
[0050] FIG. 4 is a plan view showing a first embodiment of the
optical switch according to the present invention;
[0051] FIG. 5 is a sectional view taken along the line 5-5 in FIG.
4 and looking in the direction indicated by the arrows;
[0052] FIG. 6 is an exploded perspective view of the optical switch
shown in FIG. 4;
[0053] FIGS. 7A to 7I are sectional views for explaining a method
of manufacturing an upper substrate of the optical switch shown in
FIG. 4 in sequence of manufacturing processes;
[0054] FIGS. 8A to 8G are sectional views for explaining a method
of manufacturing a lower substrate of the optical switch shown in
FIG. 4 in sequence of manufacturing processes;
[0055] FIGS. 9A to 9E are sectional views for explaining a method
of manufacturing a spacer of the optical switch shown in FIG. 4 in
sequence of manufacturing processes;
[0056] FIG. 10 is a perspective view showing a modified embodiment
of the optical switch according to the present invention;
[0057] FIG. 11 is a plan view showing a second embodiment of the
optical switch according to the present invention; and
[0058] FIG. 12 is a plan view showing a third embodiment of the
optical switch according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0059] The preferred embodiments of the present invention will now
be described in detail with reference to the accompanying drawings.
The present invention may, however, be embodied in many different
forms and should not be construed as limited to the embodiments set
forth hereinafter; rather, the embodiments are provided so that
this disclosure will be thorough and complete, and will fully
convey the scope of the invention to those skilled in the art.
[0060] First, a first embodiment of the optical switch according to
the present invention will be described in detail with reference to
FIGS. 4 to 9. This first embodiment utilizes a mirror and V-shaped
groove forming technique by use of an orientation-dependent wet
etching or chemical anisotropic wet etching as described in, for
example, the above-mentioned Japanese Patent Application No.
243582/2001 (or PCT/JP02/08177). In case such mirror and V-shaped
groove forming technique by use of the orientation-dependent wet
etching as described in the above-mentioned Japanese Patent
Application No. 243582/2001 will be used, even if the etching time
should not be controlled with high accuracy, two or four
micro-mirrors erecting from the top surface of the movable
plate-like electrode substantially at an angle of 90.degree.
thereto can be fabricated integrally with the movable plate-like
electrode with high precision. At the same time, V-shaped grooves
corresponding to the micro-mirrors can also be fabricated with high
precision at locations each forming accurately an angle of
45.degree. with the respective mirror surfaces of the
micro-mirrors. Moreover, two mirror surfaces facing each other in
the fabricated micro-mirrors forms accurately an angle of
45.degree. with each other. Accordingly, it is possible to align
each micro-mirror and each V-shaped groove corresponding thereto
with each other with high accuracy, and hence an optical signal
incident on the corresponding one micro-mirror from an output side
optical fiber can always be inputted to an input side optical fiber
by reflecting the optical signal two times by the two mirror
surfaces facing each other with high accuracy with little optical
loss.
[0061] FIG. 4 is a plan view showing a first embodiment of the
optical switch according to the present invention together with
optical fibers, FIG. 5 is a generally sectional view taken along
the line 5-5 in FIG. 4 and looking in the direction indicated by
the arrows, and FIG. 6 is an exploded perspective view of the first
embodiment of the optical switch shown in FIG. 4. The optical
switch SW3 of the first embodiment is also a 2.times.2 optical
switch having the same construction and structure as those of the
prior art optical switches already discussed with reference to
FIGS. 1 to 3, and comprises: a first substrate (hereinafter,
referred to as lower substrate) 40 of a generally rectangle in plan
that is constituted by a thick single crystal silicon layer 44 of a
generally rectangle in plan, an insulation layer (for example,
silicon dioxide (SiO2) layer) 43 formed on the top surface of the
thick single crystal silicon layer 44, and a fixed or stationary
electrode 41 of a generally square in plan formed on the top
surface of the insulation layer 43 at substantially central portion
thereof, a second substrate (hereinafter, referred to as upper
substrate) 60 of a generally rectangle in plan that is constituted
by a thick single crystal silicon layer 61 of a generally rectangle
in plan, an insulation layer (for example, silicon dioxide layer)
62 formed on the bottom surface of the thick single crystal silicon
layer 61, and a thin single crystal silicon layer 63 formed on the
bottom surface of the insulation layer 62; and a spacer 50 for
juxtaposing the lower substrate 40 and the upper substrate 60 in
parallel with each other with a predetermined space or gap
therebetween.
[0062] In this embodiment, there is prepared an SOI (Silicon On
Insulator) substrate of three layer structure comprising a thick
single crystal silicon layer 61 of a generally rectangle in plan, a
silicon dioxide layer formed on the top surface of the thick single
crystal silicon layer 61 as the insulation layer 62, and a thin
single crystal silicon layer 63 joined on the top surface of the
silicon dioxide layer 62, and the SOI substrate is used as the
upper substrate 60 by turning upside down as can be easily
understood from FIG. 5. As will be described later on, from the
thick single crystal silicon layer 61 of the upper substrate 60 can
be fabricated by use of the orientation-dependent wet etching four
thin plate-like micro-mirrors 65A1, 65A2, 65B1, and 65B2 as well as
four V-shaped grooves 64A1, 64A2, 64B1, and 64B2 in which optical
fibers 31A, 32A, 31B, and 32B are to be mounted respectively. In
case of fabricating the four thin plate-like micro-mirrors 65A1,
65A2, 65B1, and 65B2, the thick single crystal silicon layer 61
existing in the periphery of the micro-mirrors is etched and
removed in a generally square in plan, and an opening 66 of a
generally square in plan is concurrently formed in the thick single
crystal silicon layer 61. Since the four micro-mirrors 65A1, 65A2,
65B1, and 65B2 are formed at substantially the central portion of
the thick single crystal silicon layer 61, the opening 66 is also
formed at substantially the central portion of the thick single
crystal silicon layer 61, and the four V-shaped grooves 64A1, 64A2,
64B1, and 64B2 are formed on the top surface of the thick single
crystal silicon layer 61 along the longitudinal direction thereof,
two grooves being formed in parallel with each other on the top
surface of the thick single crystal silicon layer 61 at one side of
the opening 66 and the remaining two grooves being formed in
parallel with each other on the top surface of the thick single
crystal silicon layer 61 at the other side of the opening 66.
Further, in this embodiment, there is used the SOI substrate having
the thick single crystal silicon layer 61 the top surface of which
is (100) crystal face, and the orientation-dependent wet etching is
applied to this thick single crystal silicon layer 61.
[0063] On the other hand, from the thin single crystal silicon
layer 61 of the upper substrate 60 can be fabricated by
photolithography technology the movable plate-like electrode 67 of
a generally square in plan and the four flexible beams (each called
flexure) 68A1, 68A2, 68B1, and 68B2 for supporting the movable
plate-like electrode 67 to be movable toward and away from the
lower substrate 40 integrally with one another. The movable
plate-like electrode 67 is formed so as to be positioned under the
opening 66 in the thick single crystal silicon layer 61, and the
four thin plate-like micro-mirrors 65A1, 65A2, 65B1, and 65B2 are
upright from the top surface of the movable plate-like electrode
67. Consequently, the four micro-mirrors exist within the opening
66 when the movable plate-like electrode 67 is not driven. Further,
it is needless to say that the opening 66 of a generally square
formed in the thick single crystal silicon layer 61 has such a size
that it can accommodate the movable plate-like electrode 67 and the
four beams 68A1, 68A2, 68B1, and 68B2 therein.
[0064] The micro-mirrors 65A1, 65A2, 65B1, and 65B2 are fabricated
by forming four thin plate-like mirror bodies of single crystal
silicon by applying a chemical anisotropic etching to the thick
single crystal silicon layer 61 of the upper substrate 60, and
coating the wall surfaces of the thin plate-like mirror bodies with
a metal such as gold (Au), etc., or a double layer film of gold and
chromium.
[0065] Each of the four flexible beams 68A1, 68A2, 68B1, and 68B2
extends from corresponding one of the edges of the thin single
crystal silicon layer 63 opposed to each other through the opening
66 put therebetween along corresponding one of the four sides of
the movable plate-like electrode 67, two beams extending from one
edge of the thin single crystal silicon layer 63 and the remaining
two beams extending from the other edge of the thin single crystal
silicon layer 63. The free end of each beam is connected integrally
with corresponding one of the four corners of the movable
plate-like electrode 67. In this embodiment, the bases of the two
beams 68A1 and 68A2 are connected integrally with the edge of the
thin single crystal silicon layer 63 that is positioned at the left
side in FIG. 4, and the bases of the remaining two beams 68B1 and
68B2 are connected integrally with the edge of the thin single
crystal silicon layer 63 that is positioned at the right side in
FIG. 4.
[0066] Each of the four V-shaped grooves 64A1, 64A2 and 64B1, 64B2
extends from corresponding one of the opposed sides of the opening
66 to corresponding one of the opposed ends of the thick single
crystal silicon layer 61 in the longitudinal direction thereof, and
the two V-shaped grooves 64A1 and 64B2 and the two V-shaped grooves
64A2 and 64B1 opposed to one another through the opening 66 put
therebetween in the longitudinal direction of the thick single
crystal silicon layer 61 are aligned with one another.
[0067] The four thin plate-like micro-mirrors 65A1, 65A2, 65B1, and
65B2 have substantially the same shape and size with one another,
and the two micro-mirrors 65A1 and 65B1 are disposed on a first
straight line that passes through substantially the center of the
movable plate-like electrode 67 and forms an angle of 45.degree.
with a horizontal line. The remaining two micro-mirrors 65A2 and
65B2 are disposed on a second straight line that passes through
substantially the center of the movable plate-like electrode 67 and
is orthogonal to the first straight line. These micro-mirrors 65A1,
65A2, 65B1, and 65B2 are disposed at such positions that they are
away by substantially the same distance in the radial direction
from the intersection between the first and second straight lines
and that axial lines of corresponding two V-shaped grooves 64A1 and
64B2 and of corresponding two V-shaped grooves 64A2 and 64B1 pass
through substantially the centers of the micro-mirrors.
[0068] Optical fibers are located and secured in the four V-shaped
grooves 64A1, 64A2 and 64B1, 64B2, respectively. In this
embodiment, an output side optical fiber 31A and an input side
optical fiber 32A are located and secured in the V-shaped grooves
64A1 and 64A2 positioned in the left side in FIG. 4, respectively,
and in the V-shaped grooves 64B1 and 64B2 positioned in the right
side in FIG. 4 are located and secured an output side optical fiber
31B and an input side optical fiber 32B, respectively. As a result,
the output side optical fiber 31A secured in the V-shaped groove
64A1 and the input side optical fiber 32B secured in the V-shaped
groove 64B2 are opposed to and aligned to each other (are disposed
on the same optical axis line), and the input side optical fiber
32A secured in the V-shaped groove 64A2 and the output side optical
fiber 31B secured in the V-shaped grooves 64B1 are opposed to and
aligned to each other (are disposed on the same optical axis line).
Further, each of the V-shaped grooves 64A1, 64A2, 64B1, and 64B2
has its groove surface that forms a V-shape of (111) crystal
face.
[0069] The lower substrate 40 of a generally rectangle has
substantially the same shape and size in plan as those of the upper
substrate 60, and the fixed electrode 41 of a generally square in
plan that is formed on substantially the central portion of the top
surface of the insulation layer (silicon dioxide layer in this
embodiment) 43 of a generally rectangle has substantially the same
shape and size in plan as those of the movable plate-like electrode
67 and is opposed to and juxtaposed in parallel with the movable
plate-like electrode 67 with a predetermined space or gap
therebetween. In this embodiment, a plurality of minute protrusions
42 are formed, for example, in a matrix manner on the top surface
of the thick single crystal silicon layer 44, the minute
protrusions 42 being formed in the area in which the fixed
electrode 41 is formed and projecting just a little from the top
surface of the fixed electrode 41. In addition, the fixed electrode
41 is made of a double layer film of gold/chromium.
[0070] The spacer 50 is a plate-like member of a generally
rectangle in plan that has a predetermined thickness and a through
hole 51 of a generally square in plan formed in substantially the
central portion thereof. The spacer 50 has substantially the same
shape and size in plan as those of the lower substrate 40, and may
be made of, for example, a single crystal silicon substrate. The
through hole 51 of the spacer 50 is formed at a position that faces
the opening 66 of the thick single crystal silicon layer 61 and has
substantially the same shape and size in plan as those of the
opening 66.
[0071] The spacer constructed above is interposed between the upper
substrate 60 and the lower substrate 40 both constructed as
discussed above to give a predetermined electrode-to-electrode
distance or gap between the fixed electrode 41 of the lower
substrate 40 and the movable plate-like electrode 67 of the upper
substrate 60. The top surface of the spacer 50 is joined to the
bottom surface of the thin single crystal silicon layer 63 of the
upper substrate 60 with a suitable adhesive, and likewise, the
bottom surface of the spacer 50 is joined to the top surface of the
silicon dioxide layer 43 of the lower substrate 40 with a suitable
adhesive so that the upper substrate 60, the spacer 50 and the
lower substrate 40 are formed into one body and thus the optical
switch SW3 shown in FIGS. 4 and 5 is constructed. Further, instead
of using an adhesive, they may be joined to one another by use of
solder, or alternatively, by direct joining such as electrostatic
joining.
[0072] In this manner, the upper substrate 60, the spacer 50 and
the lower substrate 40 are joined and formed into one body so that
the movable plate-like electrode 67 is opposed to and juxtaposed in
parallel with the fixed electrode 41 with a predetermined
electrode-to-electrode distance (gap) therebetween and can be moved
or displaced toward and away from the fixed electrode 41 within the
opening 66 and the through hole 51 by the four beams 68A1, 68A2,
68B1, and 68B2 for supporting the movable plate-like electrode
67.
[0073] Next, a method of manufacturing the upper substrate 60
constructed as discussed above will be described in sequence of
manufacturing processes with reference to FIGS. 7A to 7I.
[0074] At first, as shown in FIG. 7A, an SOI substrate 71 of a
generally rectangle in plan is prepared by turning upside down. In
general, the SOI substrate is constituted by three layers
consisting of a support substrate of thick single crystal silicon,
an insulation layer on the top surface of the support substrate,
and a thin single crystal silicon layer on the top surface of the
insulation layer. In this example, since the SOI substrate is used
by turning upside down, in FIG. 7A, the thick single crystal
silicon layer 61 is placed at the uppermost position, an insulation
layer 62 consisting of silicon dioxide layer is formed on the
bottom surface of the thick single crystal silicon layer 61, and
the thin single crystal silicon layer 63 is joined to the bottom
surface of the silicon dioxide layer 62. The thick single crystal
silicon layer 61 has its top surface of (100) crystal face.
[0075] Next, the overall surfaces of the SOI substrate 71 are
oxidized. As a result, as shown in FIG. 7B, an oxide film (silicon
dioxide layer) 72 is formed on the top surface of the thick single
crystal silicon layer 61 of the SOI substrate 71 that is the
uppermost layer thereof, and at the same time, an oxide film
(silicon dioxide layer) 73 is formed on the bottom surface of the
thin single crystal silicon layer 63 of the SOI substrate 71 that
is the lowermost layer thereof.
[0076] Then, by use of photolithography technology, a patterning of
the oxide film 73 formed on the bottom surface of the thin single
crystal silicon layer 63 is carried out to leave portions of the
oxide film 73 corresponding to the shapes or patterns of the four
beams 68A1, 68A2, 68B1, and 68B2 and the movable plate-like
electrode 67 respectively, as shown in FIG. 7C.
[0077] Thereafter, the thin single crystal silicon layer 63 of the
SOI substrate 71 that is the lowermost layer thereof is etched
using the patterned oxide film 73 as a mask, thereby to form the
movable plate-like electrode 67 and the four beams 68A1, 68A2,
68B1, and 68B2 as shown in FIG. 7D.
[0078] Next, the remaining oxide film 73 is removed, and
thereafter, as shown in FIG. 7E, an oxide film 74 is again formed
on the bottom surface of the SOI substrate 71. Alternatively, the
overall surfaces of the SOI substrate 71 may be oxidized without
removing the remaining oxide film 73.
[0079] Then, a patterning of the oxide film 72 formed on the top
surface of the thick single crystal silicon layer 61 is carried out
to leave portions of the oxide film 72 corresponding to the shapes
or patterns of the four micro-mirrors 65A1, 65A2, 65B1, and 65B2
and the four V-shaped grooves 64A1, 64A2, 64B1, and 64B2
respectively, as shown in FIG. 7F.
[0080] Next, the thick single crystal silicon layer 61 of the SOI
substrate 71 that is the uppermost layer thereof is etched by the
chemical anisotropic wet etching using the patterned oxide film 72
as a mask, thereby to form the four V-shaped grooves 64A1, 64A2,
64B1, and 64B2 (64A2 and 64B1 are not seen in FIG. 7G) on the top
surface of the thick single crystal silicon layer 61 as well as to
form the four micro-mirrors 65A1, 65A2, 65B1, and 65B2 (65A2 and
65B1 are not seen in FIG. 7G) of the thick single crystal silicon
layer that erect from the top surface of the movable plate-like
electrode 67 through the silicon dioxide layer 62, as shown in FIG.
7G.
[0081] Then, as shown in FIG. 7H, the surfaces (including the oxide
film 72 on the top surface of each micro-mirror) of the
micro-mirrors 65A1, 65A2, 65B1, and 65B2 are coated with a double
layer film of gold and chromium to form mirror surfaces
thereon.
[0082] Thereafter, as shown in FIG. 7I, the oxide layers 72 and 74
remaining on the top surface and the bottom surface of the SOI
substrate 71 respectively are removed. Thus, the upper substrate 60
is completed.
[0083] Next, a method of manufacturing the lower substrate 40
constructed as discussed above will be described in sequence of
manufacturing processes with reference to FIGS. 8A to 8G.
[0084] At first, a single crystal silicon substrate 44 of a
generally rectangle in plan having a predetermined thickness is
prepared as shown in FIG. 8A.
[0085] Next, the overall surfaces of the single crystal silicon
substrate 44 are oxidized to form, as shown in FIG. 8B, an oxide
film 45 and an oxide film 46 on the top surface and the bottom
surface of the single crystal silicon substrate 44,
respectively.
[0086] Then, a patterning of the oxide film 45 formed on the top
surface of the single crystal silicon substrate 44 is executed to
leave portions of the oxide film 45 corresponding to the shape or
pattern of the plural protrusions 42, as shown in FIG. 8C.
[0087] Thereafter, the single crystal silicon substrate 44 is
etched by the chemical anisotropic wet etching using the patterned
oxide film 45 as a mask, thereby to form the plural minute
protrusions 42 on the top surface of the single crystal silicon
substrate 44 at substantially the central portion thereof, as shown
in FIG. 8D.
[0088] Next, the oxide film 45 remaining on the top of the
protrusions 42 is removed, and thereafter, as shown in FIG. 8E, an
oxide film 43 is again formed on the top surface of the single
crystal silicon substrate 44 including the protrusions 42.
[0089] Then, as shown in FIG. 8F, a double layer film 47 of
gold/chromium is formed on the top surface of the oxide film 43
with the chromium layer as foundation. The thickness of the double
layer film 47 is set to a value that is lower than the height (or
thickness) of the oxide film 43 covering the plural very small
protrusions 42.
[0090] Thereafter, the gold/chromium double layer film 47 is
removed except for a portion thereof corresponding to the fixed
electrode 41. At that time, the double layer film 47 covering the
protrusions 42 is also removed.
[0091] Thus, as shown in FIG. 8G, there is completed the lower
substrate 40 in which the fixed electrode 41 of a generally square
in plan is formed on substantially central portion of the single
crystal silicon substrate 44 through the oxide film 43 and the
portions of the oxide film 43 covering the protrusions 42 protrude
from the top surface of the fixed electrode 41. Further, the fixed
electrode 41 is not limited to the gold/chromium double layer film
47.
[0092] Next, a method of manufacturing the spacer 50 constructed as
discussed above will be described in sequence of manufacturing
processes with reference to FIGS. 9A to 9E.
[0093] At first, a single crystal silicon substrate 52 of a
generally rectangle in plan having a predetermined thickness is
prepared as shown in FIG. 9A.
[0094] Next, the overall surfaces of the single crystal silicon
substrate 52 are oxidized to form, as shown in FIG. 9B, an oxide
film 53 and an oxide film 54 on the top surface and the bottom
surface of the single crystal silicon substrate 52,
respectively.
[0095] Then, a patterning of the oxide film 54 formed on the bottom
surface of the single crystal silicon substrate 52 is carried out
to remove a portion of the oxide film 54 corresponding to the shape
or pattern of the through hole 51, as shown in FIG. 9C.
[0096] Thereafter, the single crystal silicon substrate 52 is
etched by use of, for example, KOH solution using the patterned
oxide film 54 as a mask, thereby to form the through hole 51, as
shown in FIG. 9D.
[0097] Next, the oxide films 53 and 54 on the top surface and the
bottom surface of the single crystal silicon substrate 52
respectively are removed as shown in FIG. 9E. Thus, there is
completed the spacer 50 of a predetermined thickness in which the
through hole 51 of a generally square in plan is formed on
substantially central portion of the spacer 50.
[0098] In such manner, the upper substrate 60, the lower substrate
40 and the spacer 50 having the same construction, structure and
shape as those of them shown in FIGS. 4 and 5 are respectively
manufactured, and the optical switch SW3 is completed by joining
the upper substrate 60 and the lower substrate 40 through the
spacer 50 interposed therebetween thereby to form them into one
body.
[0099] In the optical switch SW3 constructed as described above,
since the upper substrate 60 having the movable plate-like
electrode 67 formed thereon is joined to the lower substrate 40
having the fixed electrode 41 formed thereon by the spacer 50
interposed therebetween, the electrode-to-electrode distance (gap)
between the movable plate-like electrode 67 and the top surface of
the fixed electrode 41 is set depending upon the thickness of the
spacer 50. Accordingly, by selecting the thickness of the spacer 50
to a desired thickness, the electrode-to-electrode distance can be
easily set to a desired distance. Consequently, it is easily done
that in order to decrease the drive voltage as low as possible, the
electrode-to-electrode distance is set to a necessary and minimum
distance.
[0100] In addition, since the optical switch SW3 is constructed
such that the electrode-to-electrode distance is set by the spacer
50, there is no need to provide an elevated portion on the fixed
electrode substrate (the lower substrate) unlike the prior art
optical switches SW1 and SW2 shown in FIGS. 1 to 3, that is, the
lower substrate 40 has its flat top surface. Therefore, various
types of patternings can easily be done on the top surface of the
lower substrate 40 with high precision. As a result, it can easily
be carried out with high accuracy to form a plurality of the
protrusions 42 for preventing the sticking from occurring in a
matrix manner on the top surface of the lower substrate 40 and to
form the fixed electrode 41 of a predetermined shape on the top
surface of the lower substrate 40, as in the first embodiment.
[0101] Moreover, in this embodiment, the four micro-mirrors 65A1,
65A2, 65B1, 65B2 and the four V-shaped grooves 64A1, 64A2, 64B1,
64B2 are concurrently formed by applying the chemical anisotropic
wet etching to the same thick single crystal silicon layer 61
having its top surface of (100) crystal face. For that reason, as
described in the above-mentioned Japanese Patent Application No.
243582/2001 (or PCT/JP02/08177), or the above-mentioned paper by
Philippe Helin, et al., the vertical surface of each micro-mirror
forming at right angles with a horizontal plane becomes (100)
crystal face, and the accuracy in verticality and flatness of each
micro-mirror comes to much high. Accordingly, an input optical beam
can be reflected with little optical loss and no deviation of the
reflected optical beam occurs in vertical direction.
[0102] When the four micro-mirrors 65A1, 65A2, 65B1, 65B2, each
having its mirror surface of (100) crystal face and opposed two
mirror surfaces forming at right angles with each other, and the
four V-shaped grooves 64A1, 64A2, 64B1, 64B2 to be aligned with the
micro-mirrors for locating and securing optical fibers therein are
concurrently formed by applying the chemical anisotropic wet
etching to the same thick single crystal silicon layer having its
top surface of (100) crystal face using the identical etchant, each
micro-mirror and a V-shaped groove corresponding thereto are
aligned with each other with high accuracy. In addition, mask
patternings before the chemical anisotropic wet etching is carried
out can be done at the same time. Moreover, since the chemical
anisotropic wet etching is carried out only once, the micro-mirrors
and the V-shaped grooves can be formed at the same time by one mask
patterning and one chemical anisotropic wet etching, which results
in a remarkable improvement in working efficiency or manufacturing
process.
[0103] Furthermore, as the micro-mirrors and the V-shaped grooves
are concurrently formed by the chemical anisotropic wet etching,
the thick single crystal silicon layer is etched at the same time
using the identical etchant, and hence the etching rate for the
mirror surfaces of the micro-mirrors facing each other and the
etching rate for the adjacent V-shaped grooves 64A1, 64A2 and 64B1,
64B2 (each groove surface being (111) crystal face) in parallel
with each other can be controlled to become substantially the same
rate. Accordingly, it is possible that a deviation in the axis of
optical path due to errors in the etching rate, the etching time,
and the like is made substantially zero, and therefore, optical
beams emitted respectively from the output side optical fibers 31A
and 31B that are located and fixed in the V-shaped grooves 64A1 and
64B1 respectively can be reflected substantially perfectly by the
micro-mirrors and incident on the corresponding input side optical
fibers 32A and 32B that are located and fixed in the V-shaped
grooves 64A2 and 64B2 respectively. Further, the details thereof
will be referred to the above-mentioned Japanese Patent Application
No. 243582/2001 (or PCT/JP02/08177).
[0104] Like the first embodiment, if there is adopted the
construction in which two V-shaped grooves 64A1 and 64A2 are
juxtaposed in parallel with each other at one side of the movable
plate-like electrode 67 and two V-shaped grooves 64B1 and 64B2 are
juxtaposed in parallel with each other at the other side of the
movable plate-like electrode 67, a multi-channel 2.times.2 optical
switch can be manufactured in a small space.
[0105] FIG. 10 is a perspective view showing a modified embodiment
of the optical switch according to the present invention, and
illustrates a four channel 2.times.2 optical switch in which four
of the optical switches SW3 of the first embodiment shown in FIG. 4
are juxtaposed in parallel with one another. It is clear that the
modified embodiment of the optical switch can be manufactured by
the same manufacturing method as that of the optical switch of the
first embodiment and the same function and effects can be obtained.
Accordingly, in FIG. 10, portions and elements corresponding to
those shown in FIGS. 4 and 5 will be denoted by the same reference
characters attached thereto, and explanation thereof will be
omitted. Further, the number of channels may be changed depending
upon uses of the optical switch, and is not limited to four
channels.
[0106] In the above-mentioned first embodiment and the modified
embodiment, the four micro-mirrors 65A1, 65A2, 65B1, 65B2 and the
four V-shaped grooves 64A1, 64A2, 64B1, 64B2 have been concurrently
formed by applying the chemical anisotropic wet etching to the
thick single crystal silicon layer 61, but the micro-mirrors and
the V-shaped optical fiber securing grooves may be formed by
applying a dry etching to the thick single crystal silicon layer
61.
[0107] FIG. 11 is a plan view showing a second embodiment of the
optical switch according to the present invention. The optical
switch SW4 of the second embodiment is a 2.times.2 optical switch
having the same construction and structure as those of the optical
switch SW3 of the first embodiment already discussed with reference
to FIGS. 4 to 6 except for micro-mirrors and optical fiber securing
grooves, and so in FIG. 11, portions and elements corresponding to
those shown in FIGS. 4 to 6 will be denoted by the same reference
characters attached thereto, and explanation thereof will be
omitted unless necessary.
[0108] In the second embodiment, the thick single crystal silicon
layer 61 (not seen in FIG. 11) is etched by a dry etching to form a
micro-mirror 81 on the top surface of the movable plate-like
electrode 67 at substantially the central portion thereof through
the insulation layer 62 (not seen in FIG. 11) integrally with the
movable plate-like electrode 67. The micro-mirror 81 has a
generally cross shape (a shape formed by two line segments meeting
at right angles or St. Andrew's cross) in plan and its central
portion has a quadrangular or right prism-like shape. A first pair
of wall surfaces 82A1 and 82A2 of the generally cross-shaped
micro-mirror 81 that form at right angles with each other as well
as a second pair of wall surfaces 82B1 and 82B2 of the generally
cross-shaped micro-mirror 81 that are opposed to the first pair of
wall surfaces 82A1 and 82A2 and form at right angles with each
other are coated with, for example, gold (Au) or a double layer
film of gold/chromium to form mirror surfaces on the wall surfaces
82A1, 82A2 and 82B1, 82B2 so that the micro-mirror 81 has four
mirror surfaces. As a result, the first pair of wall surfaces 82A1
and 82A2 correspond to, for example, the mirror surfaces of the two
micro-mirrors 65A1 and 65A2 in the first embodiment respectively,
and the second pair of wall surfaces 82B1 and 82B2 correspond to,
for example, the mirror surfaces of the two micro-mirrors 65B1 and
65B2 in the first embodiment respectively. Thus, the micro-mirror
81 constructed as mentioned above functions as four
micro-mirrors.
[0109] Likewise, four optical fiber securing grooves 84A1, 84A2,
84B1, and 84B2 are formed on the top surface of the thick single
crystal silicon layer 61 along the longitudinal direction thereof
by applying a dry etching to the thick single crystal silicon layer
61, two grooves 84A1 and 84A2 being formed in parallel with each
other on the top surface of the thick single crystal silicon layer
61 at one side of the micro-mirror 81 and the remaining two grooves
84B1 and 84B2 being formed in parallel with each other on the top
surface of the thick single crystal silicon layer 61 at the other
side of the micro-mirror 81. The two optical fiber securing grooves
84A1 and 84A2 at one side and the two optical fiber securing
grooves 84B 1 and 84B2 at the other side are juxtaposed in parallel
with each other respectively, and the two optical fiber securing
grooves 84A1, 84B2 and the two optical fiber securing grooves 84A2,
84B1 opposed to each other through the micro-mirror 81 put
therebetween in the longitudinal direction of the thick single
crystal silicon layer 61 are aligned with one another.
[0110] Here, it is needless to say that the micro-mirror 81 is
formed on the top surface of the movable plate-like electrode 67 at
substantially the central portion thereof in such manner that the
mirror surfaces 82A, 82A2 and 82B1, 82B2 thereof form an angle of
45.degree. with the corresponding optical fiber securing grooves
84A1, 84B2 and 84A2, 84B1, respectively.
[0111] In case of forming the optical fiber securing grooves 84A1,
84A2 and 84B1, 84B2 by the dry etching, in general, each groove
becomes a square or quadrilateral shape groove (a groove in which
the bottom surface thereof forms a horizontal plane and both side
walls thereof stand erect from the bottom surface) or U-shaped
groove. For this reason, as shown in FIG. 11, a plurality of
springs 85 are formed on one of the side walls of each of the
optical fiber securing grooves 84A1, 84A2, 84B1, and 84B2
integrally therewith, and the optical fibers 31A, 32A, 31B, and 32B
received respectively in the corresponding optical fiber securing
grooves 84A1, 84A2, 84B1, and 84B2 are located and secured therein
by the springs 85. Further, Deep-RIE (Reactive Ion Etching)
technology can be used as the above dry etching.
[0112] A method of manufacturing the springs 85 will be described.
In case of fabricating the optical fiber securing grooves 84A1,
84A2 and 84B1, 84B2 by dry etching, spring bodies integrally with
the one side wall of a thick single crystal silicon of each optical
fiber securing groove are formed at the same time by applying the
dry etching to the thick single crystal silicon, and then, the
silicon dioxide layer 62 (not seen in FIG. 11) that is the base of
the spring bodies (to which all the bottom surfaces of the spring
bodies are connected) is removed by, for example, a wet etching.
Thus, a plurality of the elastic springs 85 integrally with the one
side wall is formed.
[0113] As the silicon dioxide layer 62 that is the base of the
spring bodies is etched, the silicon dioxide layer 62 that is the
base of the micro-mirror 81 is also etched and removed only a
little. Accordingly, it is preferred that the central portion of
the micro-mirror 81 including the crossing is formed into a
quadrangular or right prism-like pillar the area of section of
which is larger, as shown in FIG. 11, so that the micro-mirror 81
is held in the state that it is strongly secured on the movable
plate-like electrode 67 even the silicon dioxide layer 62 is
removed only a little. Further, since the micro-mirror 81 may be
one in which the area of section of the central portion including
the crossing thereof is large to a certain degree, the central
portion of the micro-mirror 81 is not limited to a quadrangular
prism-like pillar, and may be formed into a polygonal prism-like
pillar other than a quadrangular prism-like pillar, a cylindrical
pillar, a ellipsoidal pillar or the like. Alternatively, instead of
increasing the area of section of the central portion of the
micro-mirror 81, the thickness of each wall of the micro-mirror 81
on which a mirror surface is formed, may be made thick only a
little.
[0114] In the second embodiment, there has been formed on the
movable plate-like electrode 67 one micro-mirror 81 the central
portion of which is formed into a quadrangular prism-like pillar
and that has a shape of a generally cross in plan, but four thin
plate-like micro-mirrors may be formed on the movable plate-like
electrode 67 as in the first embodiment by applying the dry etching
to the thick single crystal silicon layer 61. In such case, it is
preferred to make the wall thickness of each of the four
micro-mirrors thick only a little.
[0115] Alternatively, two micro-mirrors of a generally right-angled
triangle in plan may be formed on the movable plate-like electrode
67 in a manner that they are opposed to each other by applying the
dry etching to the thick single crystal silicon layer 61, each
micro-mirror using two wall surfaces thereof forming at right
angles with each other as its mirror surfaces. In case of forming
such two micro-mirrors of a generally right-angled triangle in the
second embodiment shown in FIG. 11, the two micro-mirrors are
formed in a manner that they are opposed to each other in the
up-and-down or vertical direction in FIG. 11, and the two wall
surfaces forming at right angles with each other of one
micro-mirror of a generally right-angled triangle correspond to,
for example, the mirror surfaces 82A1 and 82B2 in the second
embodiment and the two wall surfaces forming at right angles with
each other of the other micro-mirror of a generally right-angled
triangle correspond to, for example, the mirror surfaces 82A2 and
82B1 in the second embodiment. In such case, each micro-mirror may
be one that is provided with two wall surfaces forming at right
angles with each other, and the shape of each micro-mirror is not
limited to a generally right-angled triangle.
[0116] In this way, in case of using a dry etching, micro-mirrors
of various shapes can be formed, and the shape of each micro-mirror
is not limited to shapes mentioned above. In addition, it goes
without saying that the optical fibers received in the
corresponding optical fiber securing grooves may be secured therein
by suitable fixing or securing means other than a spring.
[0117] FIG. 12 is a plan view showing a third embodiment of the
optical switch according to the present invention. The optical
switch SW5 of the third embodiment is a 2.times.2 optical switch
having the same construction and structure as those of the optical
switch SW3 of the first embodiment already discussed with reference
to FIGS. 4 to 6 and those of the optical switch SW4 of the second
embodiment already discussed with reference to FIG. 11 except that
as to a micro-mirror, one micro-mirror 81 that has a shape of a
generally cross in plan is formed by applying the dry etching to
the thick single crystal silicon layer 61 as in the second
embodiment, and that as to optical fiber securing grooves, grooves
64A1, 64A2, 64B1, 64B2 of a generally V-shape in section are formed
by applying the chemical anisotropic wet etching to the thick
single crystal silicon layer 61 as in the first embodiment.
Accordingly, in FIG. 12, portions and elements corresponding to
those shown in FIGS. 4 to 6 and FIG. 11 will be denoted by the same
reference characters attached thereto, and explanation thereof will
be omitted unless necessary. In this third embodiment, it is
preferred that the grooves 64A1, 64A2, 64B1, 64B2 of a generally
V-shape in section are, at first, formed by applying the chemical
anisotropic wet etching to the thick single crystal silicon layer
61 and thereafter, the one micro-mirror 81 having a shape of a
generally cross in plan is formed by applying the dry etching to
the thick single crystal silicon layer 61.
[0118] Since it is apparent that in the optical switch SW4 of the
second embodiment constructed as discussed above and the optical
switch SW5 of the third embodiment constructed as discussed above,
the same function and effects as those of the optical switch SW3 of
the first embodiment can be also obtained therefrom, explanation
thereof will be omitted.
[0119] As is clear from the foregoing, in accordance with the
present invention, by selecting the thickness of the spacer that is
easy in manufacture, the electrode-to-electrode distance (gap)
between the movable plate-like electrode and the fixed electrode
can be easily set to a desired distance. Consequently, there is
obtained an advantage that it is easy to set the
electrode-to-electrode distance to a necessary and minimum
distance. In addition, since there is no need to provide an
elevated portion on the fixed electrode substrate unlike the prior
art optical switches, the surface of the fixed electrode substrate
on which the fixed electrode is to be formed is flat. Therefore,
there is also obtained an advantage that protrusions, an electrode
pattern for preventing the sticking from occurring or the like can
easily be formed on the surface of the fixed electrode substrate
with high accuracy.
[0120] While the present invention has been described with regard
to the preferred embodiments shown by way of example, it will be
apparent to those skilled in the art that various modifications,
alterations, changes, and/or minor improvements of the embodiments
described above can be made without departing from the spirit and
the scope of the present invention. Accordingly, it should be
understood that the present invention is not limited to the
illustrated embodiments, and is intended to encompass all such
modifications, alterations, changes, and/or minor improvements
falling within the scope of the invention defined by the appended
claims.
* * * * *
References